Numerical simulation and validation of subsurface modification and crack formation induced by nanosecond-pulsed laser processing in monocrystalline silicon

H Kiyota,M Jankowski,M M Fejer,K Hara

doi:10.1063/1.5130701

Abstract

We describe a numerical simulation of subsurface modification and crack formation in monocrystalline silicon induced by nanosecond-pulsed laser irradiation. In this model, we assume the residual stress generation due to material transfer caused by volume reduction during melting and resolidification to be the dominant factor in creating subsurface mechanical stress and cracks. In order to quantitatively determine the geometry of the modified region, we numerically model the nonlinear propagation and absorption of the laser beam and the thermal transport. We find that during a single pulse, the lattice temperature distribution results in melting, material transfer, and structural changes on resolidification. The residual stress generated within the monocrystal adjacent to the modified region is subsequently assessed for crack formation in the substrate. The validity of the proposed model is confirmed through agreement with a number of experimental results, including the transmitted power, the timing of the onset of the phase transition during laser irradiation, the processing threshold, the geometry of the modified region, and the formed crack length.

Highlights

Subsurface laser modifications of dielectric and semiconducting materials are desired for applications in optics and electronics such as three-dimensional optical data storage[1] or the fabrication of microstructures,[2] waveguides,[3] and through-silicon-vias (TSV).[4]
We describe a numerical simulation of subsurface modification and crack formation in monocrystalline silicon induced by nanosecondpulsed laser irradiation
We proposed a model to compute the mechanical stress and the geometry of the cracks formed by subsurface nanosecond-pulsed laser modification within monocrystalline silicon wafers

Summary

Introduction

Subsurface laser modifications of dielectric and semiconducting materials are desired for applications in optics and electronics such as three-dimensional optical data storage[1] or the fabrication of microstructures,[2] waveguides,[3] and through-silicon-vias (TSV).[4]. In SD, the dicing process is executed in two steps: subsurface modification by a nanosecond laser pulse inducing crack formation in the substrate and tensile force loading to extend the initial cracks for separation of the wafer along the laser processed tracks. Infrared transmission micrography of subsurface modifications[10] and bending stress measurements of the SD-processed wafer[11] indicated that submicrosecond laser pulses could adequately induce subsurface cracks for silicon SD. This fact implies that thermal reactions dominate for crack formation in silicon wafers rather than laser-induced material embrittlement, which is likely the dominant mechanism in the femtosecond or picosecond pulse systems employed for glass SD.[8]

Methods

Results

Conclusion